The object of this proposal is the study of differentiation of secretory cell types in rodent salivary glands. With specific antisera and enzyme assays, it proposes to measure the rates of synthesis, turnover and secretion of cell type specific markers during the appearance or disappearance of the terminal tubule, acinar and granular duct cells. These studies will provide a precise biochemical description of the process of differentiation in these cells. The proposal also includes a study of the stability cf the differentiated phenotype of salivary gland secretory cells in cell culture. Preliminary studies indicate that parotid acinar cells attach and synthesize alpha-amylase for at least two weeks in culture. Using this approach, a plan is outlined which explores the cellular origins of the secretory cells and the factors which influence their appearance or disappearance.